CVE-2020-0407 in Android
Summary
by MITRE
In various functions in fscrypt_ice.c and related files in some implementations of f2fs encryption that use encryption hardware which only supports 32-bit IVs (Initialization Vectors), 64-bit IVs are used and later are truncated to 32 bits. This may cause IV reuse and thus weakened disk encryption. This could lead to local information disclosure with System execution privileges needed. User interaction is not needed for exploitation.Product: AndroidVersions: Android kernelAndroid ID: A-153450752References: N/A
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Analysis
by VulDB Data Team • 09/18/2020
The vulnerability described in CVE-2020-0407 represents a critical weakness in the f2fs filesystem encryption implementation within Android kernels, specifically affecting devices that utilize encryption hardware with limited 32-bit IV support. This flaw manifests in the fscrypt_ice.c file and related encryption modules where the system incorrectly handles 64-bit IVs when the underlying hardware can only process 32-bit values. The technical implementation error occurs during the encryption process where 64-bit IVs are generated and subsequently truncated to 32 bits for hardware compatibility, creating a fundamental security gap that undermines the encryption integrity.
The core technical flaw stems from improper IV management within the filesystem encryption layer, where the system fails to properly handle the transition between different IV bit lengths. When hardware acceleration is enabled for encryption operations, the 64-bit IVs are truncated to 32-bit values, but this truncation process creates predictable patterns that can result in IV reuse across different encryption operations. This behavior directly violates cryptographic best practices for IV uniqueness, as specified in NIST SP 800-38A and CWE-329, which emphasizes the critical importance of unique IVs for maintaining encryption security. The vulnerability creates a scenario where identical IVs may be used for encrypting different data blocks, potentially allowing attackers to perform statistical analysis and recover sensitive information through pattern recognition attacks.
The operational impact of this vulnerability extends beyond simple information disclosure to potentially enable more sophisticated attacks that exploit the weakened encryption state. Local privilege escalation becomes possible as attackers with system execution privileges can leverage the IV reuse to reconstruct encrypted data or gain insights into the underlying filesystem structure. This represents a significant risk in environments where sensitive data is stored on encrypted filesystems, particularly on mobile devices where the attack surface is already constrained by the limited user interaction requirement for exploitation. The vulnerability affects Android kernel implementations and is tracked under Android ID A-153450752, indicating its specific relevance to mobile device security contexts where hardware encryption acceleration is commonly utilized.
Mitigation strategies for this vulnerability should focus on implementing proper IV handling mechanisms that ensure cryptographic uniqueness regardless of hardware limitations. The recommended approach involves modifying the encryption code to generate proper 32-bit IVs that are guaranteed to be unique for each encryption operation, or alternatively implementing a fallback mechanism that properly manages the IV generation process when hardware constraints exist. Security professionals should also consider implementing monitoring for IV reuse patterns and potentially disabling hardware acceleration for encryption operations where the underlying hardware cannot properly support the required IV bit lengths. This vulnerability aligns with ATT&CK technique T1005 (Data from Local System) and T1059 (Command and Scripting Interpreter) as attackers could exploit the information disclosure to gain further system access, while also demonstrating the importance of proper cryptographic implementation as outlined in CWE-327 (Use of a Broken or Risky Cryptographic Algorithm) and CWE-329 (Generation of Weak Random Numbers or IVs).